The present invention generally relates to fiber optic systems and, more particularly, to a method of making a polymeric optical waveguide by coextrusion which has at least one flat side.
Fiber optics have revolutionized the communications field and are finding many applications in the medical field. Fiber optics are also providing useful in areas as diverse as computer systems, automotive systems, aerospace systems, and advertising signs. Thus, there is an ever-present need for refining and improving upon fiber optic systems for use in a wide range of industries. In this regard, the following patent applications of the assignee are hereby incorporated by reference: Larry J. Laursen, et. al., U.S. patent application Ser. No. 07/003977, entitled "A Method Of Making A Hollow Light Pipe", filed on even date herewith; Theodore L. Parker, et. al., U.S. patent application Ser. No. 07/008083, entitled "Polymeric Optical Fiber", filed Jan. 21, 1987, now abandoned in favor of Ser. No. 07/143997 filed on Oct. 8, 1987, now U.S. Pat. No. 4,834,498; and Theodore L. Parker, et. al., U.S. patent application Ser. No. 831,775, now abandoned, entitled "Polymeric Optical Fiber", filed on Feb. 20, 1986, now abandoned.
A variety of translucent/transparent materials, such as glass and amorphous polymers, have been utilized as light-conducting fibers in fiber optic systems. However, polymers offer several advantages over other fiber optic materials for applications where a small degree of signal loss is acceptable. For example, plastics have a higher numerical aperture than glass. Additionally, polymer fibers are relatively inexpensive and lightweight. They are also flexible and resistant to breakage, thereby facilitating assembly and installation. Other advantages include the fibers' immunity to electromagnetic interference. This is particularly important in automotive applications, where sophisticated multiplex data systems are subjected to electromagnetic interference generated by the alternator and spark plugs.
Light-conducting fibers in fiber optic systems are generally encased in a sheath or cladding of material having a lower index of refraction that the conducting fibers. Proper indices of refraction of the conducting material and cladding are necessary to provide a high degree of internal reflection of light traveling down the fiber and to provide an appropriate numerical aperture for the transmitting system. The greater the difference in refractive indices, the greater the numerical aperture and, thus, the more light will be trapped and transmitted through the optical waveguide. Accordingly, the lower index of refraction of the cladding relative to that of the core material enables the cladding layer to reflect light inwardly toward the core as the light travels down through the conducting core. While air has a lower index of refraction (i.e., 1.0) than any plastic material that could be used for the cladding, the plastic cladding protects the surface of the core from dust, dirt, and scratching. Thus, a plastic cladding is desirable since it can provide a smooth and continuous interface at the surface of the core, and thereby minimize the dispersion of light into the surrounding environment.
Optical waveguides are typically round in cross-section due to the currently available methods of manufacture. However, for certain uses, quadrangular waveguides would be preferable to round waveguides. For example, generally squared shaped waveguides can be made in closely packed arrays, such as shown in Schrenk, et. al., U.S. Pat. No. 3,556,635, entitled "Fiber Optic Bundle", and issued to Schrenk, et. al., on Jan. 19, 1971.
One prior attempt at making a square optical bus involved forming the core material in a mold and then coating the core with a cladding material. However, such a method would have several practical drawbacks. For example, this approach severely limits the length of fiber that can be made. Furthermore, the adhesion and interface smoothness between the cladding and core materials would be difficult to achieve with this procedure.
Thus it would be desirable to provide a method of making a polymeric waveguide which can be used as an optical bus in communication applications.
It would further be desirable to provide a method of making a polymeric waveguide which achieves a smooth and adherent interface between the cladding layer and the light conducting core.
It would additionally be desirable to provide a method of making a polymeric waveguide in the form of a polygon having at least one substantially flat side.
It would also be highly desirable to provide a continuous, high speed and, therefore low-cost, method and apparatus for producing quadrangular optical waveguides of any desired length with the above-described properties.